Rigidizing process for screens with aluminum frames

ABSTRACT

An improved process for rigidized screen for printing and the like in which the frame is zincated prior to rigidizing the screen by encapsulating the screen in nickel.

United States Patent Mentone Jan. 21, 975

[ RIGIDIZING PROCESS FOR SCREENS 2,640,789 6/1953 Hausner 204/24 WITH ALUMINUM FRAMES 2,978,389 4/1961 Tumbull Inventor: Pat F. Mentone, 1756 Eleanor St.,

St. Paul, Minn. 55116 Filed: June 15, 1973 Appl. No.: 370,326

Related US. Application Data Division of Ser. No. 198,396, Nov. 12, 1971, Pat. No.

References Cited UNITED STATES PATENTS 11/1933 Rafton 204/21 3,482,300 12/1969 Reinke 204/16 OTHER PUBLICATIONS Metal Finishing Guidebook Directory, 1968, pgs. 222-224.

Primary ExaminerR. L. Andrews Attorney, Agent, or Firm-Jacobson and Johnson ABSTRACT 1 Claim, N0 Drawings RIGIDIZING PROCESS FOR SCREENS WITH ALUMINUM FRAMES This is a division, of application Ser. No. 198,396, filed Nov. 12, 1971, now U.S. Pat. No. 3,752,187.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates generally to printing screens and methods of making printing screens and, more particularly, to rigidized self-supporting printing screens.

Description of the Prior Art There are numerous printing screens and methods of rigidizing flexible printing screens as evidenced by the Rafton U.S. Pat. No. 1,934,643, and the Reinke U.S. Pat. No. 3,482,300. Basically, these patents teach the coating of a screen to rigidize it by electrolytically coating the screen with a suitable material. For example, the Reinke patent shows a screen which is rigidized by electrolytically depositing nickel on a stainless steel screen. Reinke indicates that a uniform deposit of A to 1 mil of nickel on both faces of the screen is sufficient to rigidize the screen. While prior art processes of this type work relatively well, with screens having stainless steel frames, they are not suitable for all applications. For example, problems occur when it is desired to use a lightweight frame such as aluminum to support a screen to be rigidized. While other frames such as stainless steel are suitable, it is oftentimes preferred to use an aluminum frame for various reasons. Generally, the aluminum frame has good strength, good dimensional stability, good corrosion resistance besides being light, easy to cast, and generally less expensive than other types of frames. The use of an aluminum frame to support a screen to be encapsulated in nickel creates a problem because the aluminum is not passive in the nickel plating solution. Consequently, to plate nickel onto a screen with an aluminum frame produces a secondary reaction in the nickel plating solution that affects the encapsulating properties of the nickel. Although other encapsulating materials have been tried, it is preferred to use a final nickel finish on the screen because of its strength and corrosion resistance. Furthermore, an alternate method of using two plating materials, i.e., a first plating solution to plate onto both the aluminum and stainless steel and a second nickel plating solution to encapsulate the screen, is undesirable because the two layers of plating would substantially reduce the openings in the screen.

The present invention eliminates the problem of plating on an active metal frame such as aluminum by using two plating solutions, a first zincating solution to plate onto the aluminum frame but not onto the stainless steel screen and a second nickel plating solution to encapsulate and rigidize the screen.

SUMMARY OF THE INVENTION Briefly, the invention comprises a process and a method for producing an improved rigidized screen with an aluminum frame for use in the printing industry. In its further embodiment the invention includes an improved apparatus or screen for use in the printing industry.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment of my invention, one prepares an aluminum frame with a stainless steel screen for rigidizing by first cleaning the screen and frame. In the first step, one generally cleans the aluminum frame with a stainless steel screen in an aluminum etch cleaner. Next, the frame and screen are subjected to a spray rinse to remove any impurities or particles on the screen and frame. The screen and frame are then immersed in a nitric acid bath for approximately 30 seconds to remove any remaining impurities on the screen and frame. After the nitric acid bath, the screen and frame are subjected to a rinse of normal tap water to remove any nitric acid and thus prepare the frame and screen for the zincation step.

In the zincation step, the screen and frame are zincated for 1 minute in a zincating solution by immersing the aluminum frame and screen in the zincating solution which typically comprises sodium hydroxide and zinc hydroxide. Although sodium hydroxide and zinc hydroxide are described, other zincating solutions could also be used. During the zincating process, the outer layer of aluminum oxide is dissolved and replaced with a fine layer of zinc while the stainless steel screen remains unaffected by the zincating solution, i.e., the zinc does not plate onto the stainless steel. Care must be taken in zincating the aluminum frame to ensure that enough zinc is plated onto the aluminum frame to cover all the exposed areas of the frame. However, too long exposure to the zincating solution causes the zinc to form flakes and ridges that fall off when the aluminum frame is immersed in the nickel plating solution. Typically, l have found for a zincating solution at room temperature about one minute is sufficient time to produce a zinc coating of proper thickness.

After zincating, the screen and frame are removed and washed with a deionized water spray to remove any zincating solution on the frame and screen.

As the zincating process does not plate any zinc onto the stainless steel screen, it is apparent that at this stage the screen is uncovered while the aluminum frame is covered with a layer of zinc.

The final step to rigidize the screen requires plating nickel onto the flexible but taut screen to encapsulate the screen to thereby produce a rigid screen. In order to properly plate the nickel it is preferred to use a nickel sulfamate bath with a PH of approximately 5. The higher PI-I is desirable and preferred as it does not readily attack the zinc layer on the aluminum frame. Furthermore, with a higher PH the nickel forms a harder and stronger deposit around the stainless steel wires which produces a substantially stronger screen.

While my process is described with respect to aluminum frames, it is apparent that my process will work equally well with aluminum alloy frames and other active metal frames such as magnesium.

With my process it has also been found that the thickness of the nickel layer need only be on the order of 0.1 mil to 0.2 mil to produce a rigidized screen.

I claim:

1. The method of rigidizing a flexible printing screen mounted on a metal frame where the metal frame contains aluminum and the flexible printing screen is stainless steel comprising:

a. cleaning the aluminum frame and the stainless steel screen;

b. immersing both the aluminum frame and the stainless steel screen in a zincating solution for approximately one minute to thereby ensure that enough zinc is plated onto the aluminum frame to cover the exposed area of the frame while the stainless steel mately 5 until a nickel layer of 0.1 mil to 0.2 mil screen remains uncovered; and

c. electroplating nickel on both the stainless steel screen and the zinc coated aluminum frame in a nickel sulfamate bath having a pH of approxi- 5 thickness is obtained on the screen to thereby produce a rigidized screen.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,862,018 Dated January 21, 1975 O Inventor-( F. It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:

In the Related U.S. Application Data on page 1, column 1, line 9., "3,752,187" should be changed to --3,749,0l0

Signcd and Scalcd this Twenty-first Day of Aprill98l [SEAL] Anm:

. RENE D. TEGTMEYER Arresting Oflicer Acting Commissioner of Patents and Trademarks 

